Typical ice-cream makers of the type here considered include a blender, in which the ingredients used to make ice cream of desired flavor are homogenized, and a freezing compartment in which the resulting mixture is cooled while being continually stirred. The cooling may be carried out with the aid of a surrounding mass of ice cubes or by mechanical refrigeration. In either case, the freezing compartment is generally designed as a depressed portion of a sheet-metal plate (usually of stainless steel) forming the top of the housing which encloses the cooling unit and which may also form a seat for the associated blender; the bottom of the depression forms a boss that is traversed by a drive shaft designed to support a stirrer serving to agitate the freezing mixture.
Since the recessed freezing compartment is integral with the housing, the resulting product must be scooped out somewhat laboriously and the cleaning of the wall and bottom surfaces is not very convenient. Thus, especially with mechanical refrigeration, a water jet must not be used for this purpose since the water could pass through the boss of the compartment bottom and damage the mechanism of the cooling unit, as by entering the venting apertures of its condenser. The normal expedient of wiping the compartment with a wet rag is unsatisfactory from a hygienic point of view.
The use of a removable vessel as a container for the mixture to be frozen has been heretofore considered impractical since an ice layer tends to form at the interface between such a vessel and the surrounding compartment wall, that layer not only impeding the removal of the vessel but also inhibiting the heat exchange between the contents of the vessel and the surrounding cooling unit.